Various types of elongate members extend from a petroleum offshore structure to the seabed or to another structure. Typical elongate members include export risers, import risers, catenary risers, tension legs, transport lines, various umbilical tubes comprising an umbilical system, and bundles of cables and tethers. The elongate tubular conventionally is a metal material, although the elongate member may be fabricated from a non-metallic or composite material. In many applications, the elongate member includes a flow path for fluid, whether gas, liquid or a mixture thereof. A bundle of umbilical tubes or cables supported from a single receptacle may be considered one elongate member. Those skilled in the art will appreciate the substantial weight of these elongate members, and recognize that these members are conventionally “hung off” from the side of an offshore structure by a receptacle fixed to the structure and typically having an open throat therein for laterally receiving the elongate member. The array of elongate members may thus be organized as each member is hung off the side of the offshore structure. The term “offshore structure” as used herein is intended in its broadest sense to encompass various types of offshore oilfield production structures, including tension leg platforms, deep-draft casson systems, spars, semi-submersible vessels, and fixed or floating exploration and/or production vessels. In each case, it is conventional to attach a plurality of open throat receptacles to the hull of the structure, so that subsequently an elongate member may be laterally positioned within each receptacle and thereby be supported from the structure.
As indicated above, the elongate member imparts substantial forces to the offshore structure, and accordingly the receptacle basket itself which is fixed to the structure must be large and rugged. A surface on the interior of the basket has a receiving throat adapted for mating engagement with a similar exterior surface affixed to the elongate member. The open throat basket is generally considered essential to provide the desired flexibility so that the elongate member may be laterally positioned within the basket while it is fixed to the structure.
In addition to the size and weight of conventional baskets fixed to offshore structures, prior art baskets have other significant drawbacks. The basket is conventionally fixed to the structure with the bore in the basket at a selected azimuth and declination intended for receiving an elongate member with a planned layout. Months later, when the elongate member which is to be received within that basket has a different azimuth and declination, costly modifications to the basket are frequently required. In some cases, adapter bushings have been used to fit between an existing basket and the elongate member to achieve the desired azimuth and declination for the elongate member. Modifications to baskets already fixed to the offshore structure, including modifications accomplished with adapter bushings, may be very expensive and time consuming, and may delay the start up of the recovery operation.
The disadvantages of the prior art are overcome by the present invention, and an improved receptacle assembly for use on an offshore oilfield production structure is hereinafter disclosed. The receptacle assembly of the present invention is relatively simple, has a high reliability, and has increased flexibility compared to prior art receptacle assemblies. A new method of hanging an elongate member from an offshore oilfield production structure is also disclosed.